[clang] [lld] [llvm] Conditionalize use of POSIX features missing on WASI/WebAssembly (PR #92677)

[James Y Knight via cfe-commits]

================
@@ -45,8 +45,11 @@ void lld::unlinkAsync(StringRef path) {
   if (!sys::fs::exists(path) || !sys::fs::is_regular_file(path))
     return;
 
+// If threads are disabled, remove the file synchronously.
----------------
jyknight wrote:

There's already a check below,
```
  if (parallel::strategy.ThreadsRequested == 1)
    return;
```

Probably that should be a constant in no-threads builds, then maybe this change isn't needed?

https://github.com/llvm/llvm-project/pull/92677